Abstract

Initial stage of dynamic recrystallization (DRX) under warm and hot deformation was investigated in polycrystalline copper. At the onset of DRX at intermediate deformation temperatures (i.e., high values of Zener–Hollomon parameter Z) large orientation gradients are developed near grain boundaries, and conversely smaller gradients at high temperatures (i.e., low Z values). The frequency of thermally activated grain boundary motion coupled with various levels of local orientation gradients lead to the operation of different mechanisms of DRX nucleation. At warm deformation equiaxed grains with moderate- to high-angle boundaries are evolved at near the pre-existed boundary as a result of increasing density of geometrically necessary boundaries and progressive rotation of subgrains with little accompanying boundary migration, while at hot deformation grain boundary bulging accompanied with twinning takes place.

Schematic drawing of the nucleation of new grains under DRX. For high Z values (left-hand side) development of strain-induced geometrically necessary boundaries assisted with local lattice rotations followed by progressive transformation into high angle boundaries leads to the formation of new grains. For low Z values (right hand side) high boundary mobility leads to significant boundary serrations followed by separation of bulged parts by twinning.

TEM micrographs showing warm deformed substructures evolved in 6N Cu at T=473K and ε=1.4. (a) A colony of fine grains separated by medium- to high-angle boundaries evolved near the grain boundary (indicated by line of dots). (b) A substructure developed in grain interior. Numbers indicate the boundary misorientations in deg.

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